Four research projects are supported by this grant: (1) The objectives of the first project are to study the effects of ligand binding on the hydrodynamic properties of enzymes and how conformational change and dissociation is linked to the modifications of enzyme behavior. (2) The objectives of the second project are to learn how bi- and trivalent haptens interact with antibodies, and how the complement fixation system is activated. (3) The objectives of the third project are to measure the physical properties of very large DNA and to study the structure of intact bacterial DNA. (4) The objectives of the fourth project are to study the interaction of histones with DNA.